Since the introduction of the original “Therm-A-Rests” self-inflating mattress pad in 1971, many improvements regarding the manufacturing and resulting product have been recognized. These improvements have included modifications to production methodologies, product durability, product flexibility, and thermal performance. One goal in particular has been the reduction in the pad's weight without loss of thermal insulation performance.
In 1994, Cascade Designs, Inc. (hereinafter “Cascade”) developed a cored mattress pad that could provide a desired level of loft, but included an open cell core of foam material that had a plurality of laterally extending hollow cylinders. These transverse cylinders did not affect the bonding surfaces of the core with the enveloping sheets, but otherwise reduced the overall density of the foam core, and therefore the weight of the resulting mattress pad. However, manufacturing and performance issues, as well as the requirement for a relatively thick original core limited the range of applications for this technology.
In 1995, Cascade introduced the “UltraLite” series mattress pads. These pads were the first to utilize vertically oriented voids (i.e., orthogonal to the major surface of the core), although these voids were not the result of a material removal process. For additional information regarding this technology, please see U.S. Pat. No. 5,705,252, which is incorporated herein by reference.
A significant benefit regarding the technology used in the UltraLite series mattress pads was its ability to establish macro voids (as opposed to the open cellular construction of the expanded foam material, which constitutes micro voids) regardless of core thickness. By orienting the longitudinal axis of the voids in the vertical direction, significant density reduction of the resilient core/slab could be obtained in a relatively thin sectional thickness slab; by selectively establishing the geometry of the voids, the frequency of the voids and their overall pattern, otherwise undesirable performance characteristics of the pad could be minimized.
While the UltraLite core represented a major advance in lightweight core technology, it did result in a core having certain manufacturing disadvantages (e.g., because the voids were formed from displaced slits, and such slits usually were similarly oriented, stability of the core would be compromised in the direction perpendicular to the displacement bias). In addition, it was recognized that the vertically oriented voids provided a convenient convection and radiant heat transmission path, thereby compromising the thermal performance of the mattress pad. It was with this recognized thermal deficiency that the UltraLite core contemplated vertical voids that could buckle or collapse upon compression loading. However, creating voids susceptible to such compression buckling also compromised other performance features of the pad, such as core-to-fabric bonding characteristics and vertical support characteristics.
It thus became apparent that voids extending from the bottom to the top of a resilient core could provide a desired reduction in core weight through macro density modification without requiring a sectionally thick core. Moreover, conventional coring techniques, such as die cutting, albeit with material waste, could be used, thereby permitting use of various geometric forms to reduce slab instability that otherwise may result from the density reducing actions. However, thermal transmission mitigation means were needed in order to retain desired performance of pads incorporating such cores.